1. Field of the Invention
The present invention generally relates to a method and apparatus for allocating communication resources in a wireless communication system. More particularly, the present invention relates to a method and apparatus for efficiently allocating and employing communication resources in a wireless communication system using circuit switching and packet switching and a method for transmitting and receiving data in a mobile station using the same.
2. Description of the Related Art
Conventionally, communication resource allocation schemes for use in a wireless communication system are classified into two schemes of Circuit Switching (CS) and Packet Switching (PS). In the CS scheme, a fixed amount of radio resources, that is, a dedicated channel, is allocated to a particular user and data is transmitted and received using the dedicated channel.
FIG. 1 is a flowchart illustrating a process for transmitting data using the conventional CS scheme. An example of the conventional CS scheme for use in a transmitter of a Base Station (BS) for allocating a dedicated channel will be briefly described with reference to FIG. 1.
In step 101 of FIG. 1, the transmitter of the BS allocates the dedicated channel by performing a scheduling process for allocating communication resources to a particular user linked through a radio network. In a typical example of step 101, a particular Walsh code for identifying a channel is allocated to the particular user in a wireless communication system using Code Division Multiple Access (CDMA). In another example, particular subcarrier resources are allocated to the particular user in a wireless communication system using Orthogonal Frequency Division Access (OFDMA).
To allocate the dedicated channel, the operation for allocating the particular Walsh code or the particular subcarrier resources to the particular user is conventionally performed in a call setup or handoff process. In FIG. 1, steps 103, 105 and 107 are processes for transmitting data on the allocated dedicated channel while a call of the particular user is connected. That is, in step 103, the transmitter of the BS determines whether there is data to be transmitted to a user connected by CS (hereinafter, referred to as a CS user) for which the dedicated channel has been allocated in step 101 in an associated transmission interval. Herein, the transmission interval means a Transmission Time Interval (TTI) or frame serving as a time unit in which data of one packet is transmitted.
If data to be transmitted to the associated CS user is present in this transmission interval as a determination result of step 103, the transmitter of the BS transmits data on the dedicated channel allocated to the CS user in step 105. However, if data to be transmitted to the associated CS user is not present in this transmission interval as the determination result of step 103, the transmitter of the BS proceeds to step 105 to move to the next transmission interval. Then, the transmitter of the BS again determines whether data to be transmitted to the associated CS user is present in step 103. Until a call is terminated, the process is repeated. The communication resource allocation process based on the CS in FIG. 1 has a problem in that a dedicated channel allocated to the particular user cannot be allocated to a different user in the same transmission interval when data to be transmitted to the particular CS user is not present in the associated transmission interval.
FIG. 2 is a flowchart illustrating a process for transmitting data using the conventional PS scheme. An example of the conventional PS scheme for use in a transmitter of a BS for allocating a shared channel will be briefly described with reference to FIG. 2.
The PS scheme employs shared system resources (for example, Walsh codes of a CDMA system, subcarriers of an OFDMA system, and the like) without allocating a dedicated channel to a particular user, which is different from the CS scheme. That is, the wireless communication system using the PS scheme performs a scheduling process by determining whether to allocate system resources to a certain user in every transmission time. In step 201 of FIG. 2, the transmitter of the BS performs a scheduling process by determining whether to transmit data to a certain user in this transmission interval through an internal scheduler (not illustrated) and then allocates a shared channel to the associated user. According to a scheduling result, multiple users can be simultaneously assigned the shared channel.
An amount of user-by-user transmission data and an amount of communication resources required for a data transmission are set in the scheduling process of step 201. In step 203, the transmitter of the BS not transmits data on the shared channel allocated to the user according to the scheduling result, but also transmits shared channel control information on a Shared Control Channel (SCCH) such that the shared channel can be received. Conventionally, the shared channel control information includes a user Identifier (ID), resource information, data rate information, modulation information, coding information, and the like.
The user ID is assigned to a user in a call setup or handoff process. A Mobile Station (MS) detects the user ID from the shared control channel. When multiple users simultaneously receive the shared channel, the MS can detect its own transmitted data in an associated transmission interval. The resource information is about communication resources used for a data transmission. The data rate information indicates a transmission rate of data to be transmitted in each transmission interval. The modulation information indicates a modulation scheme used to transmit data such as Quadrature Phase Shift Keying (QPSK), 8-Phase Shift Keying (8PSK), and 16-Quadrature Amplitude Modulation (16QAM), and the like. The coding information indicates a coding method and a code rate used in a transmission process.
After transmitting control information and data on the shared control channel and the shared channel in step 203, the transmitter of the BS moves to the next transmission interval in step 205 and repeats the process from step 201 until a call is terminated.
The above-described CS or PS scheme has the following advantages and disadvantages.
First, the CS scheme is advantageous in that an amount of control information for data to be transmitted is reduced because a dedicated channel is allocated and the data is transmitted on the dedicated channel. However, the CS scheme is disadvantageous in that the efficiency of using communication resources is degraded because a different user cannot employ resources of the associated dedicated channel when there is not data to be transmitted to a user to which the dedicated channel is allocated. Further, the PS scheme is advantageous in that the throughput of a wireless communication system in which available communication resources are limited can be improved by selecting a user with a better radio channel environment, scheduling radio channel allocation, and maximizing channel-dependent scheduling gain. However, the PS scheme is disadvantageous in that a significant amount of control information should be transmitted together with data in every time because the shared channel is used. In the CS scheme, it is difficult for the channel-dependent scheduling gain guaranteed in the PS scheme to be expected.
For example, one of communication services to which the CS or PS scheme is applicable is a Voice over Internet Protocol (VoIP) service proposed to provide a voice service through an IP network. With the development of the IP network such as the Internet, the VoIP service can provide high-quality voice communication by overcoming a voice bandwidth of 56 kbps of a transmission circuit network. In the VoIP service, an overseas call can cost-effectively be used when a fee for using the Internet is paid. Further, the VoIP service can provide various application solutions and additional services. Thus, the number of users of the VoIP service is rapidly increasing.
FIG. 3 illustrates a process for transmitting voice traffic in the conventional VoIP service.
In FIG. 3, reference numeral 301 denotes an output of a vocoder for encoding an analog voice signal into a digital voice signal. As illustrated in FIG. 3, an ON period and an OFF period are divided according to whether the output of the vocoder is an output of a sound interval in which a user speaks or an output of a mute interval in which the user does not speak. A small amount of data is continuously generated in a short period (for example, 20 ms) in the conventional voice traffic. Thus, when the VoIP traffic arrives at a BS through an IP network, a received signal is irregular because VoIP packets have different IP network delay times as indicated by reference numeral 302.
The above-described CS or PS scheme is used to transmit a VoIP packet. A system for transmitting a VoIP packet in the CS scheme may not efficiently employ communication resources because a waste of communication resources is large during the OFF period as indicated by reference numeral 301 of FIG. 3. On the other hand, a system for transmitting a VoIP packet in the PS scheme transmits the VoIP packet with a small amount of data in a short period. In this case, there is a problem in that data should be transmitted together with control information for a packet reception in every time because of irregular characteristics as indicated by reference numeral 302 of FIG. 3.
Accordingly, there is a need for an improved method and apparatus for increasing system capacity and minimizing communication resources in a wireless communication system.